Wilbur l



Aug. 25, 1925. 1,551,419

W. L. MERRILL CONTRQL 0F DYNAMO ELECTRIC MACHINES Filed Nov. 7, 1922 ig 2. g 3

r- 2 g 5} a v fl d w 3 L 3 f C bl Le g h of Cable Length of c m fitor:

His Attorney.

Patented Aug. 25, 1925.

\ WILB R L. MIiRRILL,

S E 5 "!bi ,v NE Y R A ss'ienon' TO @nssnemmc con'rnon OF, amm niumsmegma-1;; 1f i To all whomli t m ay concern:

' Be it known that I, WIL UR L. MERRILL,

' a citizen of the United'States, residing at Schenectady, county of Schenectady, State 1? "provide an arrangement whereby under such 5 of New York, have 'invented certain new and useful Improvements in the Control of c porarily decreased so as'tofallow Ithe eii'ectivecabl'e length to increaseandincrease the Dynamo-Electric Machines, of which the following is a specification.

The object of my invention is providea system for controllingthe'torque of electric motorsemployed in power systems, and In particular to 'a-system for controlling the tensionona cable or the like which connects i two objects betweenwhich there is a relative motion.

o. f Although theinventionis limited thereto, it hasa particular applica-' tionin equipments for towing one objectfby' another relatively movable object, such,for

example, as towing one ship by anothen'and alsoin equipments for warping or mo oring, a ship to a'dockv e 'Due to the undulating movement of the" water, the tow line between two ships, or the mooringhline between'a dock and a ship,

tween thelength of cable; and the pull of" o is subjected to stresses which are continually I imay be within the limits of'safe operation. .A further object is tosprovide means" p as to initially connect'thetwo objects, the I distance between'which 'is-apt to vary;

varying. =As long as the undulating move-f ment is relatively-small, thevariations lIli stress in the towing or mooring line will be taken up in the catenary of the line, but for conditions such as experienced in a heavy sea, the catenary of the line can not be relied uponv to compensate for variations in the 7 distance between the line, r 7 One of the objects of theinvention isto provide an improved arrangement for autothe, objects connected by matieally compensating :for all, variations in 1 the distance separating two objects .which are connected by means of a cable, line, I

"chain, orthelike; so that the stress set up whereby the cable, line; or. other connecting device, may be'let out or taken in at ;will so Another object is to-provide means owhereby the torque offlthe towing or mooring ma-g chine may be adjusted at willsoas to ac-, V I

cable. These motors are preferablyof the" commodate for different sizes of towsand for various conditions of navigation.

I .Referr n Application filedNovenlber' 'l, SeriaITN o. 599,578: (I V i tension ofthe'cable is materially increased. Under these conditions it is: impossible to stop this action by increasing the apu'll-on the cable Anotherobject of the invention is to conditions the'pull-on' the cable will be temtorque asthe eable-is-paid out until-such tow theorigi'nal'length of cable. These and other objects ofthe-invention as'will either be apparent'to thoseskilled -in the art {or as will be explained a fully hereinafter are' attaine'din the systemogt control for dynamo electric machines whichisshown ing drawing.

"in'very simple diagram'in the accompany to:1,tlie drawing, Fig. 1 fillus *tratesih verysimple, diagram a system of motor control, embodying; the invention;

Fig." 2 represents the various relations be- .the cable Which may 'b'e obtained by'the adof'cable andthe 'cable' pullfor various 'settings of'the rh'eosta ts 'R, R and R", of Fig.

1.; and 4 represents ithe conditions which maybe obtained for decreasing the pullof the cablewhen the towedship begins to yaw,

'Referrlng to Fig. 1, the cable or other device 10 which connects the ship (not shown) which is being towed with the ship (not shown) bytwhichit is "towed, has one end connected @with the-"drum -lliso as to be wound thereon to 'vary' the "length of the cablei The apparatus. which I shall'now describe 1 is preferably {located on the ship which is'doin'g the'towing, although that is not necessary,jsince the apparatus could be locatedfon the ship Igwhich 'isf bieing towed.

fflflTheele'ctric motors112 and lame connected i-niechanically to the drum 11 by; the gearing s'hownesoj as to normally set'jupfa torque which opposes the 'ten'sion or pull of the series wound type, although they. need not necessarily be of j this type. I The'current supply for these motors is provided. by means, .01?- lthelgenerator l fwhich may be driven in any suitable manner'by any device, such for example as a steam engine or the like notshown). The generator 14 is shown as of the separately excited type having a shunt field Winding 15 which is supplied from an excitation bus 16, and the generator and motors form together a type of WVard-Leonard drive. It is to be noted that While I have shown two electric motors 12 and 13 for setting up a torque in opposition to the pull of the cable 10, my invention is not necessarily limited to such an arrangement, since asingle motor may serve the purpose. -;However, on shipboard where space is a limiting factor, it may be desir able to provide two small motors as shown in order that the drum, the gearing and the motors may he confined within a limited space.

Thec'ontr'ol of the motors '12 and 13 is eifected preferably by an "arrangement which I shall now describe whichvaries the excitation of the generator field 15 in accordance with the requirement, although the torqueof the motors may be varied in other ways as willbe understood by those skilled in the art.- The variable rheostat R is provided for adjusting the excitation of the generatorfield 15 and thus the voltage delivered by the generator 14:, so thattthe current which traverses themotor circuits will set up a torque which will practically balance the pull of thee-able for ya particular load on the cable. Thus, for example, if a comparatively light ship is beingtowed, the

greaterpart oii'therheostatR will be included in the generator'field circuit, but if.

a heavy ship is being towed, a greater amount of thislrheostat will be cut out so as to thereby increase'the torque set up by the electric motors l2 and-18. In Fig.2 I have indicated by a number of horizontal lines the variousvalues of torque which may be delivered by the electric motors to balance thepull of the cable byvarious-settings of the rheostat R i It will be understood that provided the other field controlling rheo-.

stats are not variedv and the rheostat R is set for a particular cable pull, if the effective length of cable which connects the two ships either increases-or decreases, the torque of the motors 12 and will remain substantiallyconstant, as indicated in Fig. 2. Pro vision is thus made for adjusting the towing equipmentfor various sizes of tows- It is desirable for the ordinary conditions encounteredin towing one vessel by another I that the pull'on the cable set up by the torqueof the electric. motors 12 and 13 shall increase gradually as the cable is paid out] from the drum lland gradually decrease as the cable is wound upon the drum. Such a condition is encountered when the conditions of navigation are such that the dis-' and R varying due to the undulating movements of the sea. By adjusting th rheostat R to approximately a particular value of torque as explained in connection with Fig. 2, and adjusting the'rheostat R so as to exactly cause the cable pull to be the desired value for a particular length of cable, the cable pull may be automatically increased as the length of cable: increases, and automatically decreased as the length of cable decreases by means of the automatically operated rheo stat R This rheostat is arranged to be automatically operated in response to the forward and reverse movements of the electric. motor 12 and thus in response to the paying: out and taking up oi' the cable, and in response to the tension or pull of the cable. The pull on the cable will thus be varied as indicated in dotted line, Fig. 3, for a particular setting of the rheostats R It will be observed that the rheo stat R serves as a Vernier-for the rheostat R When the movable member 17 of the rheostat R is in its upper position, the effectiye resistance of the rheost-ats R and R is the greatest, and when the movable member 17 is in thelowest position, the'rheostat R is short circuited.

In order to provide for automatically decreasing the: pull of the cable when the towed ship begins to yaw I have provided what I shall term a string relay 18. This relay comprises a contact member 19'which cooperates with the contacts 20 so as to short circuit the rheostat R in one position and with the stops 21 for limiting the movement of the member 19 in the opposite direction. The contact element '19 is mounted on, the string 22 and the ends of the string are connected by means of the take-up spring 23. The string 22 passes over the sheave 24 which is held stationary, and also over the sheave 25 which is connected to rotate with the electric motor 12- The full line arrows indicate the relative movements of the cable, drum, electric motor, rheostat element 17 and contact member 19 of the string relay when the pull of the cable predominates over the torque set up by the motors 12 and 13. The parts will be arranged so that ordinarily the torque of the electric motors will slightly predominate over the pull of the cable for ordinary conditions, so that nor mally the motors have the tendency to take up the cable rather than pay out the cable.

This condition is indicated by the dotted line arrows and it is to be understood that as indicated by the dotted line arrows. This tendency will be such that the torque of the motors merely predominates slightly over the pull of the cable but the tendency is not of sucha value that the cable is constantly being taken in. It will be observed that in ordinary conditions th contact member 19 will make engagement with the contacts and thus short circuit the rheostat R causing the pull of the cable to follow the line 26 of Fig. 4, as explained in connection with Fig. 3. When'the pull of the cable predominates over the torque of the motors l2 and 18, the string relay 18 will be operated so as to break engagement with the contacts 20 and thereby introduce the resistance of the rheostat R in the field circuit of th motor, causing the pull curve of the cable to follow the line 2'7, Fig. 4. The pull of the cable is thus momentarily decreased when the towed ship begins to yaw and cable is paid out from the drum 11. This will in many cases cause the towed ship to right itself with respect to the ship by which it is 1 being towed, and when this occurs the torque of the motors" 12 and'13 will predominate Yi ple of my invention, together with the apparatus which I now consider to represent thebest embodiment thereof but I desire to have it understood that theapparatus is only illustrative andthat the invention can be carried out by othermeans;

W hat I claim as new and desire to ses; r p v 1. The combination in a system of control for regulating the tension and the effective length of a cable or the. like, of a dynamo electric machine mechanically connected to the cable to set up a torque in opposition to the pull of the cable, means for regulating the torque of said machine, and means operated inaccordance with the movements of the machine. for automatically governing the first mentioned means to initially reduce the torque of the machine when the pull'of the cable predominates over the torque of the machine to permit the cable to be temporarily paid out and then gradu ally increase the torque of themachine as the effective length of the cable increases and decreasesthe torque of the machine as the effective length 01 the cable decreases.

2. The combination in a system of control for regulating the tension of a cable or the like, of a drum on which one end of the cable is wound, a dynamo electric machine mechanically connected to the drum to set up a torque in opposition to the pull of the cable, resistance for regulating the by Letters Patent ofthe United States,

f forregulating the tension of a' cable or the like,ofa drumto which one end of the cable is connected, a dynamo electric machine.

torque'of said machine, and means automatically operated in responseto the paying out and taking in of the cable for regulating the said resistance to reduce the torque of said machine when the pull'of said cable overcomes the torque of the machine to permit the cable to be paid out temporarily and then increase the torque of the machine as the cable is paid out. 7

3. The combination in a system of con trol for regulating the tension of a cable or the like, of a dynamo electric machine mechanically connected to the cable to set up a torque in opposition to the pull of the cable, a rheostat for regulating the torque of said machine, and means for automatically operating the said rheostat to reduce,

the torque'of the machine when the tension of the cable overcomes the torque of the machine and to then increase the torque of the machine an interval after the tension of the cable is reduced. V Y

4. The combination in a system of control for regulating the effective length and tension of a cable or the'like, of a drum to which one end ofthe cable is connected, a dynamo electric machine mechanically connected to the drum, a rheostat connected to be operated in accordance with the operation of the machine for increasing} the torque of the machine as the cable is paid out and decreasing the torque thereof as thecableistaken in, and another rheostat connected to be operated in accordance with the initial movement of the machine whenthe pull of thecable overcomes the torque of the machine for decreasing the torque of the machine to permit the cable to be paid out. 5. The combination in va system of control mechanically connected to the drum, a generator connected to supply current to the said machme to provide a. torque for governing the length and tension of the cable,

a separately excited field-for said generajtor, a rheostat in the circuit of said field for determining the normal torque of the said machine, a second rheostat operated out of saidcable for increasing the torque of Y said machine as the cable is paid out and predominates over the torque of the machine for materially reducing the torque of the machine to permit the cable to be paid out.

In witness whereof, I havehereunto set my hand this 6th day of November, 1922.

WILBUR L. MERRILL.

115 responsively to the taking up and paying 

